These pages have been constructed in fulfillment of the final project assignment for GEOS.5405 (Remote Sensing) at the University of Texas at Dallas for the fall term 2000.

Petrologic Analysis of Eastern Sultanate of Oman

by Leslie F. Bleamaster III
 

Introduction

The Sultanate of Oman is host to the Earth's largest mass of exposed ancient oceanic crust, the Samail Ophiolite.  Rock types within the ophiolite include peridiotites, gabbros, basalts, and serpentanites.  The surrounding geology is a complex collection of intensely deformed quartzites, mafic schists (including eclogite assemblages), calc-schists, dolomites and other carbonates.  Because of Oman's dry climate, lack of vegetation, and minimal cloud cover, studying the Samail Ophiolite and the surrounding area by remote sensing means is facilitated.  Three remote data sets, 1) LANDSAT (5) TM [scenes 159-44 and 158-43], 2) CORONA satellite photography [scenes DS09059A008MC028 and DS09034A023MC055], and 3) a G-topo digital elevation model (DEM), were originally proposed to be the primary, secondary, and tertiary data sets, respectfully, however, only the LANDSAT and DEM data sets proved to be useful.  Geologic mapping was based primarily on the interpretation of the two LANDSAT scenes, whereas the DEM provided a spatial context, and facilitated visualization of the ground terrain.  The DEM provided no major geologic contributions, but it did make for some very nice images.

As proposed, the results of this work were compared with the field mapping completed by Gregory, R.T., Gray, D.R., and Miller, J.M., near Masqat, Oman.  The mapping completed within this project has no where near the lithologic or structural detail achieved by the ground team, however, geologic units discerned from the remote data do correlate well with those of Gregory, Gray, and Miller.  Preliminary evaluation has raised some interesting questions and further investigation of the remote data may provide reconnaissance maps for future field studies northwest of Masqat.
 

Ophiolites

The term ophiolite refers to a distinctive rock assemblage containing ultramafic, gabbroic, and basaltic rocks, which are commonly capped by a thin veneer of deep-sea pelagic sediments.  The emplacement of ophiolites is still not well understood but certainly seems to be the result of convergence between oceanic and continental plates.  In the simplest and most straight forward model, the beginning of subduction at a newly activated old passive margin results initially in some of the ocean plate overriding the edge of the continental plate before normal subduction of oceanic lithosphere can be established.  This process, called obduction, overthrusts oceanic crust onto the continental margin and results in a cross sectional display of the uppermost layers of the oceanic crust.  This simple model does not particularly explain the processes which occured in Oman, but never the less, the ophiolite does represent ancient oceanic crust and the use of the LANDSAT 5 false color images do provide the ability to produce a simplified geologic map and statigraphic sequence for the region without ever leaving the comfort of the air conditioned lab.
 

Data

LANDSAT 5 scenes, received from Robert Gregory, were used as my primary data set.  The use of the software program ENVI, available through the UT Dallas Remote Sensing Laboratory, allowed manipulation of the spectral data.  True color (3-2-1, Figure 1) images, as well as band ratio images [i.e. Sultan's combination (5/7-5/1-3/4*5/4, Figure 2), and Abrahmís combination (5/7-4/5-3/1, Figure 3)], were all helpful in distinguishing major geologic units, however Sultan's combination (Figure2) proved to be the most valuable for differentiating lithologic differences both within and surrounding the ophiolite.

As a secondary data source I used a G-topo digital elevation model made available through the UTD Laboratory.  The DEM's spatial resolution footprint is approximately 800 meters which is much coarser than the LANDSAT's 30 meter resolution.  By generating a topo-map with 200 ft contours, it can be easily seen that the ophiolite and associated carbonate units are high standing and make up the bulk of the Oman montains that arch from the southeast to the northwest parrallelling the coastline.  The topography data also shows the two structural windows though which the basement rocks are exposed.  Although the limited resolution of the DEM does not allow for direct evaluation of topographic/lithologic relationships it can be used to enhance the LANDSAT 5 images by providing a three-dimentional spatial context.  Draping the Sultan's combination images over the DEM does show a broad corelation of lithology to topography (Figure 4).  The DEM was also used to create a 360 degree fly around above the southeastern (158-44) true color LANDSAT image (Figure 5).

Of the two mosaic CORONA scenes purchased from the USGS, only one was scanned and evaluated.  The smallness of the hard copy image (5 x 5 inches) proved to be too small to provide adequate resolution, even when scanned at the highest resolution possible.  Perhaps individual CORONA swaths, rather than mosaics would provide better resolution images.  Although the image was not used during this petrologic analysis, I am making the image available here at greatly reduced resolution (DS09034A023MC055) for you viewing.

Remote data/ Field Mapping Comparison

Using the map of the Saih Hatat by Gregory, Gray, and Miller as a guide to interpret the different colors produced by stretching the LANDSAT images (Figure 6), lithologic relationships were extended into other portions of the ophiolite to produce a simplified geologic map showing some of the large scale lithologic units and structural relationships.  More detailed studies are to come.  Please stay tuned.

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